SYNTHESIS OF NIOBIUM AND TANTALUM POWDER FROM PRODUCTS OF COMBINED PROCESS BETWEEN ALKALI FUSION AND ACID DIGESTION

• Main Author: Ranu Sirsyah, Hanajit
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/40243
• Institution: Institut Teknologi Bandung

Niobium (Nb) and tantalum (Ta) are rare metals which is classified as refractory metal that have a wide range of uses and applications in strategic technology development in the world. There are 2 types of Nb and Ta metal sources, namely primary sources which are from Nb and Ta mineral such as columbite and tantalite minerals or often abbreviated as coltan, and secondary sources from slag of tin smelting and electronic waste recycling. For producing Nb and Ta metals through pyrometallurgical route, pure feed of niobium oxide and tantalum oxide is required which is commonly synthesized by hydrometallurgical processes. The extraction process of Nb and Ta from high purity concentrates to produce high purity Nb2O5 and Ta2O5 oxides generally uses a digestion method with hydrofluoric acid (HF) followed by solvent extraction to recover Nb and Ta, precipitation Nb and Ta hydrate from strip solution strip and calcination. The extraction process using digestion with HF directly has drawbacks, among others, the products produced still contain a lot of impurities which are dissolved during the process of digestion with HF and can only be used to process high grade feeds. Because of these reasons, alternative processes continue to be investigated such as the pre-treatment process with alkaline fusion followed by leaching in water and leaching in acids (sulfuric acid and hydrochloric acid) to remove impurities in coltan before digestion with HF. In this research, the synthesis process of Nb2O5 and Ta2O5 powder was performed with a combined process, namely alkali fusion with NaOH, leaching in water and leaching in H2SO4 followed by digestion in HF, solvent extraction and recovery of Nb and Ta. By utilizing the properties of sodium Nb and Ta salts which are insoluble in water and in H2SO4 with certain concentration, impurities such as Si, Sn, Al, Fe, Ti and Mn can be eliminated in water leaching stage and sulfuric acid and the result is the feed of HF digestion with higher grade of Nb and Ta and lower content of impurities. Ore samples were obtained from the Jos Plateu Site in Nigeria through PT. Timah, Tbk. Four types of samples were received, namely primary (PR), alluvial (AL), low grade (LG) and high grade (HG). After sample preparation and sampling, sample characterization was carried out which included analysis of chemical composition by X-ray fluorescence (XRF), Inductively Coupled Plasma-Mass Spectometry (ICP-MS) and Atomic Absorption Spectrophotometry (AAS) and identification of dominant minerals in each sample with X-Ray Diffraction (XRD) analysis. A series of alkali fusion experiments, leaching in water and leaching in H2SO4 and their combinations with the HF process were carried out to study the effect of feed types (PR, AL, HG, LG and C), weight weight ratio of ore: NaOH (0.75: 1, 1: 1 and 1.5: 1) fusion temperatures (350, 450 and 550oC) and H2SO4 concentrations on the percentage of elimination of impurities, namely Al, Sn, Fe, Ti, and Mn and losses of Nb and Ta. The leaching stage aims to dissolve Sn and Al, while the leaching stage in sulfuric acid is intended to dissolve Fe, Ti and Mn. The concentration of impurity metals was analyzed by AAS, while Nb and Ta concentrations were analyzed by using ICP-MS. The results of chemical composition analysis of the samples with XRF showed that Nb and Ta contents in alluvial (AL) and primary (PR) ore are low (<0.04%). High grade sample (HG) showed a high Nb content of 47% (Nb2O5 45.3%) and Ta 4.51% (Ta2O5 3.76%). The results of XRD analysis of HG samples identified columbite (FeNb2O6) and qitianlingite ((Nb,Ta)O10) minerals as the most dominant minerals. Meanwhile, the dominant mineral in the low grade (LG) sample is cassiterite (SnO2). The results of XRD analysis of alkaline fusion products identify the phase Na(Ta,Nb)O3 which is expected to be non-souble in water and sulfuric acid. The results of alkali fusion experiments with ore type variations showed that the highest elimination percentages of Sn and Al of 51.17% and 29.91%, respectively, was obtained in the water leaching stage from the composite sample (C). The results of alkali fusion experiments with variations in the the mass ratio of ore : NaOH showed the highest Sn elimination % of 51.17% obtained at the mass ratio of ore : NaOH 1.5: 1. The experiments with the variations of alkaline fusion temperature showed that the higher the temperatures tend to enhace the elimination percentages of Sn, Al, and Mn. The highest elimination percentages of Sn, Al and Mn were 72.21%, 53.03%, and 5.93%, respectively obtained at temperature of 550oC. Leaching experiments with variations in sulfuric acid concentration did not significantly influence the elimination percentage of impurities. The higher the concentration of sulfuric acid, the higher the loss of Nb and Ta, but the losses of Nb and Ta is still under 9%. The synthesis of Nb2O5 and Ta2O5 powders with a combined process between alkali fusion and digestion with HF was able to obtain high purity of Nb2O5 and Ta2O5 powders with the highest content of Nb2O5 and Ta2O5 of 90.01% and 84.66%, respectively, with total impurities contents in the forms of Al, Fe, Mn oxide, Ti and Si under 1%.